For reasons of good efficiency, gas turbines today have operating temperatures in the hot gas region in excess of 1400° C. It is therefore not surprising that many components of the gas turbines, such as for example moving blades, stationary blades or combustion chamber linings, are exposed to great thermal but also mechanical loads. Since these components are usually produced from expensive high-temperature materials, it is desirable to repair them instead of completely replacing them when they are damaged. In addition, there is often a need to upgrade already installed components, in order to improve their efficiency or adapt them to changing operating conditions.
EP 1 620 225 B1 describes a method for repairing and/or modifying components of a gas turbine in which first at least a portion of the component to be repaired or to be modified is extracted, in particular cut out, from the component. Subsequently, at least the first time this portion of the component is repaired or modified, a data record is created for a replacement part to be produced. The replacement part is then produced by means of a rapid manufacturing process.
After, or even before, the extraction, in particular cutting out, of the particularly damaged portion, and possibly of a tolerance portion adjoining the damaged portion, from the component to be repaired, a data record is created for the replacement part to be produced. In this connection, first a three-dimensional CAD data record is created for the replacement part to be produced. This 3D CAD data record for the replacement part to be produced is subsequently converted into a machine data record. First it is checked whether a 3D CAD data record for the component to be repaired or modified but in the undamaged state or a corresponding new part exists. It is disadvantageous here that an individual distortion (or distortion of a series) cannot be taken into account by the operation. There is always a discrepancy (mismatch) between the actual geometry at the time and the nominal geometry. If such a 3D CAD data record for the undamaged component exists, it is subsequently checked whether firstly there is systematic damage to the component and whether secondly the geometry of the damaged component is reproducible. In the case where there is systematic damage to the component and at the same time the geometry of the damaged component is reproducible, it is possible by taking as a basis statistical evaluations of the size of the damaged portion of the component to be repaired and taking into account during the repair a tolerance portion adjoining the damaged portion, the previously damaged regions of material and greatly stressed regions of the component to deduce the required geometry of the replacement part to be produced and to generate the 3D CAD data record from it.
If, on the other hand, there is no systematic damage to the component to be repaired and/or the geometry of the component that is damaged or to be modified is not reproducible, a reverse engineering of the component, or at least of the relevant regions of the component, is carried out. For carrying out the reverse engineering of the component or component region, first the particularly damaged portion and possibly in addition the tolerance portion adjoining the damaged portion is/are extracted from the damaged component to be repaired. This is followed by performing measurements on the component or component region, for example by mechanical or optical measured-value pick-ups or by computed tomography and subsequent reverse engineering. A 3D CAD data record of the component or component region that is damaged or to be modified, from which the damaged portion and possibly a tolerance portion have previously been extracted, is obtained as a result. From this 3D CAD data record of the worked component or component region, the 3D CAD data record of the replacement part to be produced is determined by establishing the difference in comparison with the 3D CAD data record of the undamaged component.
However, such reverse engineering is altogether very laborious.
WO 2008/034413 describes a method of repair for moving blades of a gas turbine in which a damaged portion of a damaged blade tip is removed by forming a parting surface and then the removed portion is reconstructed on the parting surface by means of a generative process (rapid manufacturing) using three-dimensional CAD structural data of the blade. Such a method of repair entails considerable restrictions concerning the choice of material and the geometry.
WO 2008/046386 describes the building up of a complete gas turbine component by such a rapid manufacturing method.
General methods for creating three-dimensional parts to which reference is made further below in the course of the description are described in, for example, EP 946325, DE 10219983, EP 1358855, U.S. Pat. Nos. 6,355,086, 6,811,744 and 7,537,722.